1. Field of the Invention
This invention relates to a membrane electrode unit for fuel cells, membrane electrolysis units and membrane compressors, which consists of a polymer electrolyte membrane and electrodes covering the latter on both sides, as well as a reinforcing frame attached to the periphery of the membrane electrode unit.
2. Description of the Prior Art
In similar membrane electrode units of the prior art, the electrodes have a porous catalyst layer attached to a backing material and are covered with gas distributors and current leads and have a frame-like reinforcement to facilitate handling and installation. The reinforcement of the individual units makes installation significantly easier, especially when there are a plurality of membrane electrode units arranged in series in a fuel cell unit that have installation borings and openings for the passage of the coolant and reaction medium, as well as corresponding seals in this inactive area.
On a similar membrane electrode unit of the prior art that is described in U.S. Pat. No. 5,187,025, the reinforcing frame is formed by two electrode frames that are in tight contact with the electrodes, between which electrode frames, extending into the membrane electrode unit in the form of a frame bridge, there are plastic layers and a plastic membrane layer (membrane frame) which also extends into the membrane electrode unit, whereby the connection between the electrode frames and the frame bridge or the frame bridges and/or between the membrane frame and the polymer electrolyte membrane is created by means of a thin acrylic adhesive layer. However, on account of its reinforcement, this membrane electrode unit, which is advantageous for the manufacturing of fuel cells on account of its reinforcement, has the disadvantage that it is also difficult and expensive to manufacture on account of the many individual parts, and in any case the handling of adhesives in the manufacturing process presents problems of its own, because the surface energy of the polymer used as the backing material is low, and it is therefore difficult to achieve good adherence.
The object of the invention is therefore to create a membrane electrode unit of the type described above which can be manufactured easily and economically and guarantees a secure seal of the electrochemical cell.
The invention teaches that this object can be achieved with a membrane electrode unit that consists of a polymer electrolyte membrane and electrodes that cover it on both sides, as well as a reinforcing frame that is attached to the periphery of the membrane electrode unit, wherein the reinforcing frame is formed by a hot-melt-type adhesive layer that is deposited on both sides in the outer peripheral area and in the peripheral area of openings that are provided for installation and/or to guide media and a rigid plate which is attached to the hot-melt-type adhesive layer on one or both sides, whereby the hot-melt-type adhesive layers can be connected by the action of pressure and heat with the rigid plate(s) and the membrane electrode unit into a one-piece reinforcing segment in the peripheral area in question.
The hot-melt-type adhesive layers, which on the outer peripheral reinforcement preferably extend beyond the outside edge of the membrane electrode unit, are pressed against the rigid plate and the membrane electrode unit, thereby compensating for any irregularities and differences in thickness, penetrate deep into any cavities that
may be present and thereby enter into an intimate connection with each other and with the membrane electrode unit and the rigid plate(s) in the projecting area. Therefore, with only a few components, a homogeneous and inherently stable reinforcement segment is created which can be manufactured easily, guarantees easy handling of the membrane electrode unit and provides a secure seal of the electrochemical cell in the outer peripheral area as well as in the vicinity of openings to guide media.
Additional characteristics and advantageous developments of the invention are described in greater detail in the dependent claims and in the following description of one preferred exemplary embodiment of the invention.
For example, one important feature of the invention is that the hot-melt-type adhesive layers extend by approximately one-half of their width beyond the outer edge of the membrane electrode unit, so that the hot-melt-type adhesive layers can be melted directly together in this area, thereby reducing the amount of material required for the membrane electrode unit, of which only a narrow edge is covered.
The invention also teaches that a hot-melt-type adhesive with ionic or strong polar groups is used which enter into an intimate interaction with the ionic groups of the polymer electrolyte membrane and therefore guarantee a good adherence of the hot-melt-type adhesive to the membrane.